Okay kiddo, so you know how sometimes we use a calculator to solve math problems, right? Well, when a computer program is being made, the program also needs to solve problems and do various things to work properly.
However, sometimes, instead of using a calculator, the program can do some of the problems on its own before it even starts running! This is called "compile-time function execution".
Just like how we solve math problems one step at a time, a computer program also has certain "steps" or "instructions" it needs to follow in order to solve a problem. These steps are called "functions".
Usually, when a program is run, it follows these steps ("functions") in order to solve a problem. However, with "compile-time function execution", some of these functions are done before the program even starts running! It's like solving part of the math problem before we even write it down on the paper.
This can be helpful because it makes the program run faster and also makes it easier to catch certain errors before the program even runs.
So basically, "compile-time function execution" means doing some of the work before the program starts running, kind of like solving part of a math problem before we write it down.